Proposal Summary/Abstract Project Title: Mechanisms of Behavior Change in Culturally Adapted Motivational Interviewing The NIAAA Five Year Strategic Plan prioritizes health disparities research for socially disadvantaged Latinos to reduce the disproportionate burden of negative consequences related to alcohol use compared to other racial/ethnic groups (NIAAA, 2013/2016). Cultural adaptation of evidence-based treatments, such as motivational interviewing (MI), can improve access and overall response to alcohol treatment. However, research progress has been hindered by the few theoretically-guided tests of adaptation and limited knowledge about the active ingredients and mechanisms of behavior change that might discriminate an adapted, compared to non-adapted, intervention. The proposed study will fill this important gap by testing a series of theory-driven hypotheses regarding the within-session predictors of MI outcome and a novel mechanism of culturally adapted MI (CAMI) (self-exploration ? decreases in perceived acculturation stress, reduced depression and anxiety ? reduced heavy drinking and consequences). The proposed study codes and examines within-session, process data from a parent RCT (AAR01021136, Lee: PI) guided by adaptation theory initially tested in a small RCT (AAK23021136, Lee: PI) that showed promising effects in favor of CAMI (Lee et al., 2013). The ongoing parent CAMI trial compared single session MI to single session CAMI delivered to Latino heavy drinkers (N=301, 18-65 yrs old). The parent study design (e.g., assessment of multiple self-report mediators) permits examination of a causal model, while attending to key recommendations on examining mechanisms of change (Kazdin & Nock, 2003). Up-to-date statistical approaches will be used to examine the MI causal hypothesis, such as investigating change and sustain talk together as a proportion estimate (Magill et al., 2014). The parent study design, which used an active comparator (MI), permits between-condition tests of within-session ingredients and mechanisms, which is a level of contrast rare in MI theory and one of the first a- priori investigations of processes of change in an adaptation study. The first task in adaptation is to confirm that key active treatment ingredients and mechanisms are preserved, so study aims are first, to assess MI ingredients and mechanisms among Latino adults, second, to examine novel MI ingredients and mechanisms potentially relevant to both conditions, and third, to test the theory, ingredients, and mechanisms specific to the adaptation. Long term objectives. Findings will improve dissemination of MI to Latinos by providing empirically-based guidelines on therapist training and on critical MI intervention ingredients. It will also improve understanding of the stress-health behavior link observed among health disparities populations and how MI can be used to disrupt this association. The proposed study will be one of the first to contribute to the emerging science on mechanisms of behavior change with health disparities populations and will yield important recommendations on the science of adaptation and ways to improve MI dissemination to community settings.